Flow control shrink wrap tunnel

ABSTRACT

A heat shrink tunnel has at least one wall in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and a perforated plate to feed air from the discharge chamber to the interior of the tunnel. Structure is provided adjacent to each hole in the baffle plate to compound the turbulence in air passing from the supply chamber to the discharge chamber thereby to equalize the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber.

United States Patent [191 Evans, Jr.

Feb. 18, 1975 FLOW CONTROL SHRINK WRAP TUNNEL [75] Inventor: Stephen M. Evans, Jr., Dallas, Tex.

[73] Assignee: ITP Corporation, Dallas, Tex.

[22] Filed: Mar. 7, 1974 [21] Appl. No.: 449,053

[52] US. Cl 34/216, 34/231, 34/233,

53/184 S [5 l] Int. Cl. F26b 19/00 [58] Field of Search 34/218, 221, 224, 225,

34/226, 230, 23l234, 105, 33, 34, 216, 217; 53/305, 184 S; 98/40 R, 40 V, 40 VM;

[56] References Cited UNITED STATES PATENTS 3,388,479 6/l968 Gardner 34/160 3,574,952 4/l97l Lee, Jr 34/105 3.6l6,548 ll/l97l Nichols .4 34/233 Primary Examiner-Kenneth W. Sprague Assistant ExaminerJames C. Yeung Attorney, Agent, or 'FirmRichard, Harris & Medlock [57] ABSTRACT A heat shrink tunnel has at least one wall in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and a perforated plate to feed air from the discharge chamber to the interior of the tunnel. Structure is provided adjacent to each hole in the baffle plate to compound the turbulence in air passing from the supply chamber to the discharge chamber thereby to equalize the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber.

10 Claims, 7 Drawing Figures FLOW CONTROL SHRINK WRAP TUNNEL This invention relates to the control of the flow of heated air into tunnels through which palatized products pass and over which heat shrinkable material is placed for giving integrity to the pallet plus its contents.

In the prior art systems, shrink wrap tunnels provide a flow of heated air directed onto palatized materials covered with heat shrinkable sheet material. In U.S. Pat. No. 3,616,548 a system is disclosed wherein a stated objective is to distribute heated air against the top and sides of the heat shrinkable material with substantially equalized volume and velocity for uniform shrinkage of the material around the articles. In that system, a supply chamber extends around the two sides and the top of the tunnel. Perforations lead from the supply chamber to a perforated discharge chamber with particular relationships'being specified in the orientation of the perforations leading from the supply chamber to the discharge chamber and from the dis charge chamber into the tunnel.

The control of the air flow in such shrink wrap tunnels and particularly from the top of the tunnel with such structure disclosed insaid patent has been found to be lacking in the uniformity of flow.

U.S. Pat. No. 3,577,651 discloses a system for heating, drying or cooling sheet material surfaces as the material is passed through an open-sided treating station. The system comprises two plenum chambers, one above and the other below the sheet material. Each chamber receives pressurized hot air which is directed from a chamber through a first perforated discharge member of a nozzle structure and thence through a second perforated discharge member of the structure to be distributed transversely across the material surface. Particular relationships between the perforations on the discharge members are specified to improve uniformity of air flow across the material to be treated.

Though the structure disclosed in U.S. Pat. No. 3,577,651 provided an improvement over prior art, deleterious effects from uneven air flow persisted.

The present invention is provided in order to overcome the limitations present in prior art systems such as represented by U.S. Pat. Nos. 3,616,548 and 3,577,651. More particularly, in accordance with the present invention, the flow of heated air to the supply chamber is maintained at a sufficiently high pressure that there is uniform distribution of flow throughout the entire supply chamber with structure provided adjacent to the holes leading from the supply chamber to the discharge chamber which induce substantial turbulence in the flow of air passing through the holes. This assures even distribution of air flow throughout the discharge chamber of air which passes from the discharge chamber into the tunnel. In a preferred embodiment, a tunnel is provided with at least the top structure as herein described. In a further aspect, the top and both side walls are similarly constructed to provide such turbulent flow at supply pressure.

For a further understanding of the invention and for a more complete description thereof, reference may now be had to the following, taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a heat shrink tunnel system;

FIG. 2 is a cross-sectional view ofthe supply chamber and discharge chamber relationships as taken along lines 2-2 of FIG. 3;

FIG. 3 is a sectional'view taken along the lines 33 of FIG. 2;

FIG. 4 is a cut away view showing structure employed for creating turbulence;

FIG. 5 is a top view of one unit with the top plate and baffle plate successively cut away to show the relationship between the perforations in the baffle plate and in the lower plate;

FIG. 6 illustrates a modified form of structure for turbulent flow; and 1 FIG. 7 illustrates a still further modification.

FIG. 1 illustrates a shrink tunnel 10 in which the present invention is embodied. Tunnel 10 comprises side walls 11 and 12 with a top 13 defining a passageway 14 through which a conveyor 15 passes. Motor 16 drives a fan in a chamber 17 in which heated air is directed to the interior of tunnel 10.

A perforated side wall 18 is shown in FIG. 1 through which the air is directed to contact heat shrinkable film to be placed around the materials on a pallet passing through tunnel 10.

In accordance with the present invention, at least the top wall of tunnel 10 is provided with a turbulence producing structure to distribute the air uniformly within a chamber behind panel 18 so that there will be a uniform distribution of hot air immerging into tunnel 10, thereby to avoid the creation of hot spots and undesirable deterioration of the packaging film.

In accordance with the present invention, the top inside wall of tunnel 10 (preferably the top wall and both side walls) are provided with a dual plenum structure in which hot air flow from a supply chamber to a discharge chamber is caused to have a significant degree of turbulence resulting from special structure employed at the passageway between the two chambers. In FIG. 2, structure for directing supply of heated air into tunnel 10 of FIG. 1 has been shown. A dual chamber system is formed in which the top plate 20 is parallel to a baffle plate 21 below which there is positioned a lower plate 22. Heated air is directed into the chamber between the plates 20 and 21 at pressure sufficiently high to produce uniform distribution of 'air throughout chamber 23. A plurality of holes are provided in the baffle plate 21 for flow of air from chamber 23 to chamber 24. A plurality of smaller holes are then provided in plate 22 for flow of air from chamber 24 into the tunnel 10.

FIG. 3 illustrates one form of structure for producing turbulent flow upon passage of air from chamber 23 to chamber 24 and the relationship of the passage to the ports in the bottom plate 22. More particularly, plate 21 has a rectanglar opening 30 therein. In this embodiment, hole 30 is formed by establishing two slits at right angles to one another and then bending down into the chamber 24, the tabs formed so that around opening 30, the four tabs such as the tabs 31 and 32 extend down into chamber 24. The axis 35 of the hole 30 is intermediate to axes 36 and 37 of holes 38 and 39 in the bottom plate 22. The flow of air from chamber 23 through the irregular short tube formed by the tabs 31 and 32 causes the air to spill into chamber 24 with compounded turbulence by reason of the flow generated forces on and around tabs 31 and 32.

FIG. 4 more graphically illustrates the structure involved. It will be noted that the four tabs 31-34 form the side walls of a duct of irregular length around the perimeter of hole 30. The flow of air through the rectangular hole 30 produces flow generated forces on the airstream to be turbulently distributed into chamber 24 above the plate 22 and thus provides uniform flow through holes 38, 40 and 41.

The geometrical relationship ofv the system is shown in FIG. 5 wherein top plate and baffle plate 21 both have been partially cut away. It will be noted that rectangular hole and an array of like holes are formed in a uniform pattern extending along lines 51, 52, 53, etc. Preferably, the square holes have centers spaced apart along lines and 51 half the distance between the lines 50 and 51. Below lines 50 and 51 of holes in plate 21 are rows of holes such as the hole 40 in plate 22. Holes 40 are on a grid which is the same dimension as the spacing between the holes along line 50. The axis of hole 30 lies at the center of a four hole array in the bottom plate 22.

An opening 54 is formed in the top plate 20 through which air is directed by a fan and deflected by baffle 55 into chamber 23. v

A modified form of turbulence creating structure is shown in FIG. 6 where more elongated tabs 61-64 form side walls adjacent to the opening in the baffle plate 21. This type of side wall structure, suitably secured as by rivets or tack welds 65, provides baffle control producing turbulence by reason of the flow generated forces on the tube which is of uneven length around its perimeter.

FIG. 7 illustrates a further embodiment in which a hole through plate 21 has a secondary baffle unit 71 positioned therebelow in theform of a dish having an uneven edge 72. The baffle unit 71 is secured by legs 73 and 74 immediately below the hole 70 so that the flow of air is given significantly wide and turbulent distribution in the chamber 24.

Thus, in accordance with the present invention, a dual chamber supply system is provided wherein one chamber is a supply chamber, the second is a discharge chamber with a baffle plate between them having an ordered array of ports through the baffle plate not aligned with ports throughthe discharge plate. Structure adjacent each hole in the baffle plate induces compounded turbulence in the flow of air passing from the supply chamber to the discharge chamber, thereby to equalize the volume and velocity of air flowing through perforations in the discharge plate.

In one embodiment where the structure of FIG. 5 was 78 by inches and the height of chambers 23 and 24 were 2 inches and 4 inches, respectively, the supply chamber had an internal static pressure of 1.5 inches of water.

Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What is claimed is:

1. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and an output perforated plate leadingfrom the discharge chamber, said baffle and output plates being positioned in a spaced parallel relationship, the combination which comprises:

a. structure adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, and

b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.

2. The combination according to claim 1 in which each of said holes in said baffle plate is provided with a portion extending into said discharge chamber.

3. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and an output perforated plate leading from the discharge chamber, the combination which comprises:

a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, each said tubular extension is of uneven length around its perimeter, and

b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.

4. The combination according to claim 2 in which each said hole in said baffle plate is rectangular.

5. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises:

a. atubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, said extensions are formed by bending down into said discharge chamber portions of said baffle plate, and

b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.

6. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises:

a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, said extensions comprise side bars secured to said baffle plate adjacent to the edges of each said hole and extend down into said a discharge chamber, and

b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.

7. The combination according to claim 6 in which said barsare of uneven length.

8. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises:

a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, a secondary baffle unit is supported below each said hole in said baffle plate, and

b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.

9. The combination according to claim 8 in which said secondary baffle unit has the form'of a dish with an uneven, upward turned edge.

10. The method of control of heat in a shrink tunnel through which pass articles to be served by a heat treated film, comprising:

introducing a flow of heated air into a first zone isolated from said tunnel by a second zone;

flowing said air from said first zone to said second zone via a plurality of restricted uniformly arrayed paths while subjecting the flow in said paths to flow generated forces which vary along the lengths and around the perimeters of said paths to create turbulence as said air enters said second zone; and delivering air from said second zone to said tunnel via a plurality of uniform paths. 

1. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and an output perforated plate leading from the discharge chamber, said baffle and output plates being positioned in a spaced parallel relationship, the combination which comprises: a. structure adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, and b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.
 2. The combination according to claim 1 in which each of said holes in said baffle plate is provided with a portion extending into said discharge chamber.
 3. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber and an output perforated plate leading from the discharge chamber, the combination which comprises: a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, each said tubular extension is of uneven length around its perimeter, and b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.
 4. The combination according to claim 2 in which each said hole in said baffle plate is rectangular.
 5. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises: a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, said extensions are formed by bending down into said discharge chamber portions of said baffle plate, and b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.
 6. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises: a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, said extensions comprise side bars secured to said baffle plate adjacent to the edges of each said hole and extend down into said discharge chamber, and b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.
 7. The combination according to claim 6 in which said bars are of uneven length.
 8. In a heat shrink tunnel through which the articles pass and in which a supply chamber is flow connected to the interior of said tunnel by way of a perforated baffle plate leading to a discharge chamber, said holes in said baffle plate being rectangular, and an output perforated plate leading from the discharge chamber, the combination which comprises: a. a tubular extension adjacent to each hole in said baffle plate to compound turbulence in air passing from the supply chamber to the discharge chamber for equalizing the volume and velocity of air flow through the perforations in the plate leading from the discharge chamber, a secondary baffle unit is supported below each said hole in said baffle plate, and b. perforations in said output plate whose axes are spaced from the axes of holes in said baffle plate.
 9. The combination according to claim 8 in which said secondary baffle unit has the form of a dish with an uneven, upward turned edge.
 10. The method of control of heat in a shrink tunnel through which pass articles to be served by a heat treated film, comprising: introducing a flow of heated air into a first zone isolated from said tunnel by a second zone; flowing said air from said first zone to said second zone via a plurality of restricted uniformly arrayed paths while subjecting the flow in said paths to flow generated forces which vary along the lengths and around the perimeters of said paths to create turbulence as said air enters said second zone; and delivering air from said second zone to said tunnel via a plurality of uniform paths. 